Frozen Embryo Transfer (FET)

Frozen embryo transfer (FET) is the thawing of an embryo that was frozen and stored earlier, and its transfer to your uterus in a suitable cycle. The preparation of your uterus is carried out in a natural or medicated way. When the approach of freezing all embryos and transferring them later is compared with fresh transfer, it is likely that there is little or no difference in live birth; some signals of difference related to pregnancy and birth, on the other hand, remain uncertain for now. The information here draws a general framework; it does not replace a diagnosis or treatment recommendation specific to you.

What is frozen embryo transfer (FET)?

The embryos formed in IVF treatment can be transferred in the same cycle, or they can be frozen and used in a later cycle. FET is the transfer stage of this second path. Frozen transfer makes up an important part of IVF treatments today, and its use has increased over time. IVF treatment is carried out within Ota Jinemed and Liv Hospital Ulus, with the laboratory and embryology teams of these hospitals.

In which situations is FET performed?

FET can be considered for various reasons:

• Postponing the transfer if your ovaries responded excessively to stimulation and your risk of ovarian hyperstimulation syndrome (OHSS) is high.
• Waiting for the result if genetic testing was applied to the embryos.
• The conditions of your uterus not being suitable for transfer in that cycle.
• Using frozen embryos left over from a previous cycle.

Your doctor determines which reason applies to you.

How is the transfer procedure performed?

The transfer of the frozen embryo is performed in the same way as a fresh transfer, with a thin catheter and under ultrasound guidance. The difference of FET from fresh transfer is the thawing of the embryo and the way your uterus is prepared.

How is the uterus prepared for FET?

How is a natural cycle applied?

In a natural cycle your own ovulation is taken as the basis. The timing of the lining of your uterus and of your ovulation is followed with blood tests and ultrasound; the transfer is planned accordingly. It can be chosen in people who ovulate regularly.

How is a medicated (programmed) cycle applied?

In a medicated cycle, the lining of your uterus is prepared with hormone medicines given from outside and the day of transfer is set according to the plan. Side effects related to the hormone medicines may be seen.

How is the preparation method chosen?

Natural and medicated preparation each have their own advantages and disadvantages. Factors such as whether your ovulation is regular, how your previous cycles went and your preference are taken into account. In studies comparing these two approaches, no definite superiority has been shown; your doctor makes the choice.

Fresh or frozen? What does the evidence say?

Is there a difference in terms of live birth?

Studies on this subject show that between the approach in which all embryos are frozen and transferred later and conventional fresh transfer, there is either no difference in live birth or the difference is very small. It has not yet been settled that freezing increases the chance of live birth, nor is there any finding that it reduces it. So at present there are not enough data to say whether freezing all embryos or fresh transfer is better.

Is there a difference in terms of pregnancy and birth outcomes?

The same studies report that with the approach in which all embryos are frozen, problems with high blood pressure in pregnancy (including pre-eclampsia) and a high birth weight of the baby may be seen slightly more often; these findings rest on data not yet considered strong. It has also been observed that the average birth weight of babies born after frozen transfer is slightly higher. These signals are not a definite conclusion; you plan your pregnancy follow-up together with your doctor.

Is freezing all embryos (freeze-all) recommended for everyone?

Current assessments do not recommend freezing all embryos in every couple; there are no strong data to support it. But if your risk of OHSS is high, this approach has its place; it is known to be useful in reducing the risk of OHSS.

What happens when the embryo is thawed?

The embryos are thawed for the day of transfer and it is assessed whether they have survived. Not every embryo is expected to survive thawing; the likelihood of survival varies from person to person and from embryo to embryo.

What are the risks of frozen embryo transfer?

• Medicine side effects: Bloating of the abdomen, headache and mood changes related to the preparation medicines may be seen.
• Multiple pregnancy: It increases with the number of embryos transferred. Current guidelines recommend single embryo transfer, which also applies to FET.
• Ectopic pregnancy: A pregnancy formed with a frozen embryo can also be ectopic.
• Bleeding and infection: Light spotting can occur.
• Clotting (thrombosis): It can be seen, although rarely, in people using hormone medicines.

What happens after FET?

In FET cycles the risk of OHSS is lower than in a fresh cycle. After the transfer you may see light spotting, mild pain similar to period pain and a feeling of fullness in the abdomen. The day of the pregnancy test is told to you by your doctor and it is done as a blood test; home tests done before this day can be misleading.